1. Field of the Invention
The present invention relates to a PTT (Push-To-Talk) communication system for performing PTT communications, a PTT communication method, and a PTT communication server.
2. Description of the Related Art
In recent years, there have been proposed many PTT communication systems for performing PTT communications using terminals (see, for example, JP-A-07-074669). Of the PTT communication systems, a PTT communication system which employs cellular phones as terminals is referred to as a POC (PTT Over Cellular) communication system.
In the PTT communication system, when a user belonging to a certain group wants to begin a PTT communication session, the user logs in a PTT communication server with its own terminal, confirms another terminal belonging to the same group, and requests the other terminal to join the PTT communication session through the PTT communication server. If the other terminal agrees to join the PTT communication session in response to the request, then the requesting terminal and the joining terminal participate in the PTT communication session and start transmitting communication data to each other. PTT communication services allow a single terminal to communicate with another single terminal and also allow a single terminal to communicate simultaneously with a plurality of (N) terminals.
In a PTT communication session, when a user presses the PTT button of its own terminal to obtain a token, i.e., a right to speak or communicate, from the PTT communication server, only that user can send communication data, i.e., audio and/or video data, from its terminal through the PTT communication server to another terminal or other terminals, just like using a transceiver. When the user with the token releases the PTT button and another user presses the PTT button of its own terminal, the other user who is pressing the PTT button obtains a token from the PTT communication server.
According to the conventional PTT communication systems, only terminals equipped with PTT buttons can join PTT communication sessions, and servers that are not equipped with PTT buttons are not allowed to join PTT communication sessions.